1. Field of the Invention
The present invention relates to an automatic focusing device, more particularly, to an automatic focusing device in which a focusing distance range can be set by a photographer.
2. Description of the Related Art
In a conventional automatic focusing device provided in an automatic focusing single-lens reflex camera, a distance measuring zone is formed in a field of vision of a vie finder of the camera, so that the photographer can determine on which part of an object the camera lens is focused. The object light coming into the distance measuring zone is divided into two parts, which are fed to a measuring sensor having CCD, and a focusing calculation is carried out by a focusing control unit to obtain a defocus amount and direction. An AF motor is driven according to this vector value, and the photographing lens is moved to a position at which the object is in focus.
The driving of the above automatic focusing device is started by a half depression of a release button. In a servo AF, when the release button is partly depressed, a distance measuring operation and a focusing operation for the photographing lens are carried out at predetermined intervals.
When a photograph is to be taken by the above conventional automatic focusing camera, if the object to be photographed moves out of the distance measuring zone, the camera is controlled to focus on a new object coming into the distance measuring zone. Especially, when a moving object is to be photographed, often the object to be photographed can not be followed correctly and moves temporarily out of the distance measuring zone. In such a case, if another object coming into the distance measuring distance zone is positioned at infinity or within a short distance, the photographing lens is moved to infinity or to the short distance focusing position. Therefore, even if the former moving object again moves into the distance measuring zone, a long time is required to move the photographing lens to a position at which the moving object is in focus. When photographing a moving object, usually the camera must be operated very quickly, and if a long time is required to focus the lens on the object to be photographed, then chance to take a desired photograph is often lost.
In particular, when a moving object is to be photographed by using an ultra-telephotographic lens, in which the focusing time is normally long, the above problem readily occurs.